Recently, the increasing demand for computers, particularly personal computers (hereinafter abbreviated as “PC”), in response to an explosive expansion of the Internet has caused the industries in the field to develop rapidly. The market has demanded products of higher performance and lower costs, which leads to a fierce competition on the supply side that has been trying to meet the demand. One of the significant factors in determining the performance of a computer is a storage device, and the mainstream of the same is a semiconductor memory configured so that memory cells are formed on a semiconductor substrate such as silicon. The main requirements for the high performance of the semiconductor memory are “high speed of input/output to/from memory”, “large capacity of memory”, and “stability of storage”. Computers may have various configurations to meet various demands of the market, but in the case where both of the higher speed and the larger capacity are pursued, the cost rises, whereas in the case where a compromise is made by giving up either of the two, the cost can be reduced.
Currently, the most common memories built in PCs are configured so that cache memories and main memories are composed of RAMs (random access memories), and examples of memories used as such include DRAMs (dynamic random access memories) and SRAMs (static random access memories).
A DRAM has a larger capacity per unit area as compared with a SRAM and is manufactured at a lower cost, whereas it has a problem that an output of memory takes time since the retrieval of memory is carried out by discharging electric charges, and moreover, the supply of charges (refresh) is required at all times.
On the other hand, in the case of a SRAM, since the retrieval of memory therefrom is carried out by determining a state of a multivibrator, refreshing is not required, and the reading is performed at a high speed. However, because of a complex structure thereof, the SRAM has a smaller capacity per unit area, and is expensive, as compared with a DRAM.
Therefore, a common memory configuration in a PC is such that a SRAM is used as a cache memory and a DRAM is used as a main memory so that the cost is suppressed. Further, since the memory in the DRAM and SRAM disappears when the power is turned off, necessary memory has to be stored in another storage device such as a disk. Examples of storage devices in which memory is not lost even after the power is turned off include a flash memory, but considering its need for high voltage upon input, its limited capacity, and its cost, it hardly satisfies the above-described demands of the market at the present time.
For the downsizing and speed enhancement of a computer, a storage device in the computer has to have a large capacity. As to a DRAM as a typical internal memory, the dense packaging has been attempted by reducing the cell size, but insufficient capacity of a capacitor has been a problem. More specifically, though various cell structures have been studied for increasing an electrode area, they are significantly complex structures, and there arise problems such as an increase in the cost per one bit and an increased ratio of defects that occur during manufacturing.
As a conventional example, a scheme for recording/reproducing information in/from a medium by detecting current flowing through an element with use of a probe electrode has been proposed, the medium being obtained by laminating a recording film having an electric memory effect on an amorphous carbon layer formed on a substrate electrode (JP 5(1993)-28549A).
However, in the foregoing scheme, the organic film is not chemically bonded with a surface of a substrate and is separated therefrom easily. Additionally, it needs further improvement regarding electric characteristics.